This disclosure relates to improved self-locking or ligatureless orthodontic brackets.
Orthodontic treatment generally comprises dental work to correct irregularities of the teeth or of the relation of the teeth to surrounding anatomy. The irregularities may involve malocclusions with varying degrees of severity. Class 1 malocclusions, for example, may involve spacing irregularities such as excessive crowding or diastema (a gap between two adjacent teeth). Class 2 malocclusions may involve overbite conditions where the upper anterior teeth project labially over the lower anterior teeth. Class 3 malocclusions, in contrast, may involve underbite conditions where the upper anterior teeth close within the lingual side of the lower anterior teeth. For these and other observed irregularities treatment typically involves installation of braces or mechanical aids for repositioning the teeth into correct orthodontic alignment.
Braces generally include orthodontic brackets configured for attachment to the labial or lingual surfaces of the teeth or for attachment to metallic bands secured around the teeth. The brackets typically include archwire slots within which a flexible yet resilient archwire may be engaged. Each bracket is typically bonded to the tooth surface so that the bracket's archwire slot is oriented for engagement with the archwire. Various techniques are used for orienting the brackets. For example, an edgewise appliance comprises braces whereby each bracket is oriented and bonded to the tooth so that the archwire slot is perpendicular to the long axis of the root of the tooth. Alternatively, a straight-wire appliance includes braces whereby each bracket is oriented and bonded to the tooth so that the archwire slot is parallel to the occlusal plane (the biting surfaces of the teeth).
The archwire is typically a curved metallic wire having a rectangular or circular cross section that is bent or twisted prior to engagement with the brackets. The memory or restoring force exerted by the archwire upon the brackets serves to move the teeth into the desired alignment. Throughout the duration of orthodontic treatment the orthodontist periodically adjusts the shape of the archwire (as well as the configuration of other attachments such as elastic bands and so forth) to achieve the correct orthodontic alignment.
Most brackets in current use incorporate tie wings or extensions that project upwardly and downwardly in a gingival-occlusal orientation and require the use of ligatures or ligating modules to hold the archwire within the archwire slots. The ligatures or ligating modules are typically donut-shaped elastomeric rings or wires that are stretched around or twisted around the tie wings.
The use of such ligatures or ligating modules presents a number of inherent disadvantages, some of which are mentioned herein. The small size of the ligatures or ligating modules requires substantial time for installation of the archwire. Because the orthodontist will typically make numerous adjustments to the archwire throughout orthodontic treatment, the orthodontist will likely remove and replace the ligatures or ligating modules numerous times. Hygiene is another problem since the use of ligatures or ligating modules increases the areas where food particles may be trapped. Further, with movement due to chewing or other activities, the ligatures or ligating modules may become detached altogether, allowing the archwire to disengage from the archwire slots.
Ligatures or ligating modules also present other limitations in terms of the forces exerted upon the brackets. For example, the labial or outward force that may be applied to a tooth having a bracket bonded to its labial surface is limited to the strength of the ligature or ligating module in the labial direction. On the same tooth, the force that may be applied in the lingual direction is not so constrained (because the force is applied against the bracket structure rather than the ligature or ligation module). Similarly, the longitudinal (or mesial-distal) forces which may be applied along the direction of the archwire may be limited or defined by the friction between the ligature or ligation module and the archwire. By contrast, a means for locking the archwire within the archwire slot would enhance the forces that may be exerted along the direction of the archwire. Likewise, a means for slideably retaining the archwire within the archwire slot would allow greater flexibility than available from brackets requiring the use of ligatures or ligation modules.
Several self-locking or self-ligating (ligatureless) orthodontic brackets have been designed. However, most of those have complex designs, incorporating features requiring prohibitively expensive machining operations or comprising multiple separate parts, which in turn increases the number of failure modes for such brackets. Other designs have been rejected in the marketplace due to poor quality or poor design, a lack of available features, difficulty of use, or other factors.
What is needed, therefore, is an improved orthodontic bracket that incorporates a self-ligating capability and that offers a different style of bracket than those available today.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.